M100907 is an orally active, potent, and highly selective 5-HT2A antagonist with biochemical and pharmacological properties that may provide therapeutic benefit for the treatment of psychosis. The primary objectives of this study are to continue the safety evaluation of M100907 in the treatment of subjects with schizophrenia or schizoaffective disorder who participated in Protocol HMR 3001. The secondary objectives of this study are to: 1) evaluate the long-term efficacy of M100907 as monotherapy for symptom control in subjects with schizophrenia and schizoaffective disorder who participated in Protocol HMR 3001. 2) to continue to evaluate the effects of M100907 on the cognitive deficits associated with schizophrenia and schizoaffective disorder. 3) to assess the impact of M100907 on quality of life scores longitudinally using the Heinrichs-Hanlon-Carpenter Quality of Life Scale (QLS) and the Scale to measure Subjective Well-Being Under Neuroleptic Treatment (SWN). 4) to measure the impact of M100907 resource utilization associated with long-term treatment with M100907. This is a multicenter, long-term, safety follow-up, open-label trial of once-daily dosing of M100907 as monotherapy in the treatment of subjects with schizophrenia or schizoaffective disorder. The GCRC nursing staff will assist with performing EKG's, collecting blood and urine samples, and sample processing.